Such a process is disclosed for example in International patent application WO 91/16269. According to that process, a minimum ratio between sulphide and biomass is used.
International patent application WO 92/10270 discloses a cyclic process for the removal of sulphur compounds from a gaseous effluent wherein an aqueous solution is alternately contacted with the gaseous effluent and subjected to sulphur-oxidizing bacteria. Elemental sulphur formed by the bacterial oxidation is separated off from the aqueous solution, in such a way that 0.1 to 50 g of elemental sulphur per l is left in the recycled aqueous solution.
All known processes for bacterial waste water treatment are faced with the problem of keeping the bacteria inside the reactor. This problem is usually solved by using a carrier material for the bacteria. Two types of carriers are generally proposed: (1) mobile carriers such as pumice; however, a disadvantage of mobile carriers is that a vigorous turbulence or fluidization must be maintained in order to keep them mixed with the waste water to be treated, and, furthermore, a part of the mobile carrier will interfere with the sulphur formed, which is detrimental for the quality of the sulphur; (2) fixed carriers such as structures of synthetic material; they have a disadvantage that these fixed carriers get clogged up quickly. Moreover, both the conventional mobile carriers and the conventional fixed carriers considerably increase the cost for operating the treatment plant.